Snap-acting fluid motor



Jan. 20, 1953 J, w, JACOBS 2,626,183

SNAP-ACTING FLUID MOTOR Filed June 23, 1951 NIH IN 5 UL ATION FIG. I

INSULATION FIG. 2

I N VEN TOR. 72

Patented Jan. 20, 1953 SNAP-ACTING FLUID MOTOR James W. Jacobs, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application June 23, 1951, Serial No. 233,181

7 Claims. 1

This invention relates to electrical apparatus and more particularly to fluid pressure operated control means such as may be used for temperature and pressure control purposes.

To obtain snap-action operation in response to slowly fluctuating pressures applied to fluid motors, it has been customary to provide a mechanical detent arrangement such as a toggle device for delaying movement and building up energy in the fluid motor until snap-action movement is assured.

It is an object of my invention to control the application of fluid pressure to the fluid motor in such a way that snap-action takes place without the use of mechanical detent arrangements.

It is another object of my invention to delay the application of slowly fluctuating fluid pressures to a fluid motor until the pressure is built up to an amount suflicient to assure snap-action.

It is another object of my invention to provide a simple double-acting valve means connected between a fluid motor and a force of slowly fluctuating pressure, which valve means will be controlled by the fluid motor to prevent the application f the slowly fluctuating fluid pressures until the pressure diiierences are suflicient to assure snap-action movement.

These objects are attained by providing a control device in which the fluid motor is in the form of a metal bellows which has its open end sealed to a valve seat structure which is adjustably supported by the frame. A double-acting valve is provided in the valve seat structure and connected to the closed end of the bellows. One valve seat opening communicates directly within the bellows while the second valve seat opening c nnects to a thermostatic fluid pressure element. Externally the bellows may be connected to any suitable control device such as a switch or a valve mounted upon the frame.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanyin drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a vertical sectional view to one form of control means shown at the closed position, embodying my invention; and

Fig. 2 is a similar fragmentary sectional view showing the control in the open position.

Referring now to the drawings there is shown a U-shaped frame 28 having supported between the ends of its legs a switch block 22 of electric insulating material. Extending through the 2 block 22 is an electric terminal 24 having it outer end connected by the conductor 26 to one terminal of an electric motor 28, the other terminal of which is connected to one of the supply conductors 38. The inner or lower end of the terminal 24 has fastened to it a cantilever-type spring contact member 32 which, at the opposite end, carries a movable switch contact 34 adapted to engage a normally stationary switch contact 36 upon the inner or lower end of the adjustable terminal 38 which is provided with threads 40 so that it may be threaded through the block 22 and turned to adjust the position of the contact 35. The terminal 38 is connected to the supply conductor 42.

To operate the cantilever blade type switch member 32, there is provided a fluid motor in the form of a metal bellows 44. The lower or open end of this metal bellows 44 is sealed to the rim of an enclosed double valve seat structure 46. This valve seat structure 46 is provided with a bearing portion 48 extending through the hollow screw 50 which is threaded through an extruded threaded aperture 52 in the yoke of the frame 2%. The screw 5% is provided with a splined lower end on which is mounted an adjusting knob 54 held in place by a C-type washer 56. By rotating the knob 54, the valve seat structure 46 and the bellows 34 are raised or lowered relative to the frame 29 as well as the switch member 32.

The valve seat structure 45 has its principal portion in the form of a cylinder containing a valve chamber 58. Within the upper portion of this valve chamber 53, there is provided a valve seat through which extends the valve seat opening 62 providing communication between the valve chamber 58 and the interior of the bellows 44, At the bottom of the chamber 58 there is provided a second valve seat 64 directly opposite the valve seat 65 and similar in size and shape. However the valve seats 60 and 84 may be different in size and area and are proportioned in efiective areas to the opening and closing pressures desired. Concentrically located with the valve seat 64 is a valve seat opening 66 which connects directly with a capillary tube 68 extending through the bearing portion 48 and being sufliciently long to reach to any point to which it is desired to apply this capillary tube. This capillary tube 58 may be connected to any source of control pressure or as illustrated, where it may be charged with .a suitable amount of volatile liquid and sealed so that it serves as a thermosensitive element.

Occupying the closed portion of the space within the valve chamber 58 is the valve member 70 provided with a thick facing 12 and 14 on each side which may be of any suitable form of synthetic rubber such as neoprene. The valve member '10 is provided with a valve stem 16 connected directly to the closed upper end 18 of the bellows 44. The closed upper end 18 of the bellows is connected by the fitting 80 and the link 82 of electric insulating material to the switch member 32.

This structure operates with a snap-action through this valve arrangement which provides for a sudden release of the pressure dififerential to suddenly expand and suddenly contract the bellows 44. The operation may be explained as follows: in Fig. 1 the valve member ID has its face 14 in sealing engagement with the upper seat 60 thereby closing the passage 62 communicating with the interior of the bellows 44. At the time of closing there will be a pressure within the bellows 44 which is above atmospheric pressure. This will tend to expand the bellows 44 and hold the valve 19 tightly against the seat 60. The bellows 44 and the switch member 32 will therefore remain in this position until this upward pressure force within the bellows 44 has been overcome. To overcome this upward force within the bellows 44, which is equal to the pressure differential between the pressure within the bellows 44 and the atmosphere upon the eiiective area of the bellows, it is necessary to apply an equal downward force in the opposite direction to peratures of the thermo-sensitive element 68 thereby reducing the pressure gradually within the thermosensitive element 68 and the valve chamber 58. When the temperature within the tube 58 has become low enough that the pressure upon the effective areas of the lower face of the valve member produces a downward force greater than the total amount of upward force upon the closed end 18 of the bellows 44, then the bellows 44 will immediately collapse with the snap-action and immediately move the valve 10 into the position shown in Fig. 2, wherein the lower face 12 is in sealing contact with the valve seat member 64 to seal the lower valve seat opening 66.

In causing this collapse of the bellows 44 the pressure within the thermo-sensitive element 68 must have been reduced below atmospheric pressure. Consequently, the atmospheric pressure on the outside of the bellows 44 is greater on the inside of the bellows 44 providing a downward or collapsing force which holds the lower face 12 of the valve 10 firmly in contact with the lower seat 64. This shuts off communication between the thermo-sensitive element 68 and the interior of the bellows 44. However, the opening of the contacts 34 and 36 causes the temperature of the thermosensitive element 68 to rise slowly. Both the temperature and pressure rise within the thermo-sensitive element 68, and after suficient time, become greater than the pressure within the bellows 44 and applies a greater force directly onto the valve member 10. When the pressure in the thermosensitive element 68 becomes high enough to provide a force on the valve member 10 in the upward direction sufficient to overcome the pressure differential between the atmosphere acting on the outside of the bellows 44 and the pressure existing on the inside of the bellows 44, then the valve member 70 will be forced oil the seat 64 and returned to its original position in Fig. 1 with a snap-action. Such a control can be substituted in a great many cases for controls of the type employing a mechanical detent arrangement. This type of control may be used in a great many places where a mechanical detent arrangement is objectionable.

As one specific example, assume that the seats 60 and 64 have an area of 1 square inch each.

Also assume that the bellows 44 has an effective area of 2 square inches. To place the piston 10 in sealing engagement with the seat 60, there must be a pressure within the bellows 44 which is greater than the atmospheric pressure. It is assumed in this example that this excess pressure in the bellows is 1 ounce per square inch. This makes the gross expansion force within the bellows 2 ounces per square inch which is opposed to the piston 70 a mounting to 1 ounce per square inch providing a net force of 1 ounce in the upper direction on the end wall 18 of the bellows 44.

To collapse the bellows then, the pressure within the capillary tube 68 must be reduced sufficiently to provide a force slightly greater than the 1 ounce of force in the opposite direction on the end Wall 18. Therefore to make the bellows collapse, because the valve 76 has only 1 square inch of effective area, the pressure within the capillary tube must be reduced to a pressure of 1 ounce per square inch below the atmospheric pressure. When this pressure is reached, the valve 10 will begin to move away from the seat 60. As soon as this takes place, gas will quickly rush out from the interior of the bellows 44 past the valve 10 and the valve seat 60 into the valve chamber 68 into the capillary tube 68, thereby rapidly reducing the pressure in the bellows 44 .to 1 ounce per square inch below the atmospheric pressure. The atmospheric pressure acting on the outside of the bellows 44 will then quickly collapse the bellows and move the valve l6 into engagement with its lower seat 64.

The pressure in the bellows at the time the valve l0 moves in sealing engagement with the seat 64 will be 1 ounce per square inch less than the atmospheric pressure. If the pressure within the bellows 44 is now 1 ounce per square inch below atmospheric pressure, then the downward force of the bellows 44 will be 2 ounces while the pressure on the piston it! will be 1 ounce making a net force of 1 ounce on the closed end 78 of the bellows 44 in the downward direction. The bellows 44 will remain in this collapsed position until there is a suflicient rise in pressure within the capillary tube 68 to lift the piston 73 off its seat 64. Under the assumed conditions, a pressure of 1 ounce per square inch in the capillary tube 68 will force the valve 70 oh? the seat 64. As soon as gas can rush by the valve '14 and the seat 64 it will fill the interior of the bellows 44 to a pressure of 1 ounce per square inch above atmospheric pressure, thereby causing the bellows 44 quickly to expand and return to the position shown in Fig. 1. V

The above analysis is based on the assumption that the inherent spring effect of the bellows 44 and the contact member are at all times substantially equal and opposite to each other so that they cancel out. If this is not the condition, the bellows exerts an upward inherent spring force, the eifective area of the upper seat 60 must be enlarged an amount equal to the arithmetic sum of the upward spring forces in the contact closed position of the bellows id and member 32 divided by the total operating pressure differential. The effective area of the lower seat 64 must be reduced by an amount equal to the arithmetic sum of the upward spring forces in the contact open position of the bellows 44 and member 32 divided by the total operating pressure differential.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. In combination, a fluid motor means, a first valve seat and valve seat opening connecting with the interior of said fluid motor means, a second valve seat and valve seat opening adapted to be connected to a fluctuating absolute pressure, and a valve means operably connected to said fluid motor means for making sealing engagement with said first valve seat in one direction of movement and for making sealing engagement with said second valve seat in the opposite direction of movement.

2. In combination, a fluid motor means, a first valve seat and valve seat opening connecting with the interior of said fluid motor means, a second valve seat and valve seat opening, means forming a valve chamber connecting said first valve seat and valve seat opening with said second valve seat and valve seat opening, a fluid connection connected to the opposite side of said second valve seat and valve seat opening from said valve chamber, a valve means having two valve surfaces located in said valve chamber adapted to move alternately into sealing engagement with either the first or second valve seat, and an operative connection between said fluid motor means and said valve means for moving said valve means into contact with said first seat upon expansion of the fluid motor means and for moving said valve means into contact with said second seat upon contraction of the fluid motor means.

3. In combination, a fluid motor means, a first valve seat and valve seat opening connecting with the interior of said fluid motor means, a second valve seat and valve seat opening, means forming a valve chamber connecting said first valve seat and valve seat opening with said second valve seat and valve seat opening, a fluid connection connected to the opposite side of said second valve seat and valve seat opening from said valve chamber, a valve means having two valve surfaces located in said valve chamber adapted to move alternately into sealing engagement with either the first or second valve seat, and an operative connection between said fluid motor means and said valve means for moving said valve means into contact with said first seat upon expansion of the fluid motor means and for moving said valve means into contact with said second seat upon contraction of the fluid motor means, said fluid connection being in the form of a sealed tubular member containing a means to change the pressure therein in accordance with temperature.

4. In combination, an enclosed fluid motor means, a fluid connection providing a fluctuating absolute pressure connected to the interior of the fluid motor means, a valve means having two valve seats and two valve surfaces connected in series between said fluid connection and the interior of said fluid motor means, and an operative connection between said fluid motor means and said valve means for moving the valve surfaces into a first alternative position upon expansion of the fluid motor means and into a second alternative position upon contraction of the fluid motor means.

5. In combination, an enclosed fluid motor means, a fluid connection providing a fluctuating absolute pressure connected to the interior of the fluid motor means, a valve means having two valve seats and two valve surfaces connected in series between said fluid connection and the interior of said fluid motor means, and an operative connection between said fluid motor means and said valve means for moving the two valve surfaces into a first alternative position upon expansion of the fluid motor means and into a second alternative position upon contraction of the fluid motor means, said fluid connection being in the form of a sealed tubular member containing a means to change the pressure therein in accordance with temperature.

6. In combination, a bellows, a double valve seat structure located within the bellows and sealed to the open end thereof, a fluid connection connecting with one valve seat in said structure, the second valve seat in said structure being connected to the interior of said bellows, said valve seats in said structure being connected in fluid connection with each other, and a double acting valve member operably connected to the closed end of said bellows and being located between said seats for engaging said seats in sealing engagement.

7. In combination, a fluid motor means, a first valve seat and valve seat opening connecting with the interior of said fluid motor means, a second valve seat facing in the opposite direction to the first valve seat, said second valve seat having a valve seat opening, a first fluid connection connecting the openings in the first and second valve seats, a valve means having a first valve surface for engaging and sealing the opening of said first valve seat, said valve means also having a second valve surface facing in the opposite direction to the first valve surface for engaging and sealing the opening of said second valve seat, an operative connection between said fluid motor means and said valve means for moving said first valve surface into engagement with said first valve seat upon expansion of the fluid motor means and for moving said second valve surface in the opposite direction into engagement with the second valve seat upon contraction of the fluid motor means, and a second fluid connection connected to the opposite side of the second valve seat from the first fluid connection.

JAMES W. JACOBS.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 1,842,337 Te Pas Jan. 19, 1932 2,102,656 Vaughn Dec. 21, 1937 2,113,351 Lear Apr. 5, 1938 2,501,730 McClure Mar. 28, 1950 

